Null value in asp net

The nullable value types are available beginning with C 2. Any nullable value type is an instance of the generic System. You typically use a nullable value type when you need to represent the undefined value of an underlying value type. For example, a Boolean, or bool , variable can only be either true or false.

However, in some applications a variable value can be undefined or missing. For example, a database field may contain true or false , or it may contain no value at all, that is, NULL. You can use the bool? As a value type is implicitly convertible to the corresponding nullable value type, you can assign a value to a variable of a nullable value type as you would do that for its underlying value type.

You can also assign the null value. For example:. HasValue property returns false. Beginning with C 7. You always can use the following read-only properties to examine and get a value of a nullable value type variable:.

HasValue indicates whether an instance of a nullable value type has a value of its underlying type. Value gets the value of an underlying type if HasValue is true. The following example uses the HasValue property to test whether the variable contains a value before displaying it:. A better way to return HTTP status is to use action filter or result filter, as shown in the following code:. You can put this filter at the action level, controller level or global level.

If you want to put it at the global level, you can add the following code in the configureservices method of startup:. When using asp. After the action returns data, the bottom layer of the framework will do necessary serialization operations on your returned results.

However, when action returns a null value, asp. In other words, the framework will return HTTP status , indicating that the request is successful but there is no content. Fortunately, you can change the default behavior as needed. NET in the following code where dr is a datareader :.

Here is an example in C of using a DataTable and using the IsDbNull function to set a text field while looping through the rows. NET code to your database. Here is how you would set your object variable to DBNull.

Value in either C or VB. I specialize in Web application development with a focus on building secure systems, integrating applications, and designing robust database structures. View all posts by Justin Cooney. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. However, a null value can present challenges when you are working with ASP. NET code or with data-bound Web controls.

For example, an exception is thrown if you try to bind the SelectedValue of a DropDownList control to null.

NET provides some built-in functionality for working with null values. If your scenario is not solved using the built-in ASP. NET capabilities, there are some additional techniques you can use for working with null values. You can set the NullDisplayText property of bound fields in data source controls such as the BoundField , CheckBoxField , and ImageField objects to substitute a specific value such as a string for null values returned from the data source. Controls will then display that value as the text of the bound control.